1. Field of the Invention
The invention relates to a fiber mat for producing a three-dimensional, molded molding by the dry process.
2. Description of the Prior Art
The production of three-dimensional molded moldings from lignocellulose fibrous materials by loosely sprinkling onto an endless conveyor belt the fibers wetted with small quantities of binder levelling the height for the fiber layer applied by a pairing roller and subsequently prestrengthening the fiber layer between pairs of rollers is known. This process leads to a sheet-like endless extrudate which can be cut into individual sheets from which flat blanks are produced following intermediate transport. Following vapor coating of the blanks, they are placed in a compression mold and are formed into the final molded articles, accompanied by the curing of the binder (DAS No. 1,224,949). The individual sheets cut in this way initially have a low deformability and limited breaking strength. Following the vapor coating necessary to increase the deformability for producing the three-dimensional molded molding articles, the sheets no longer have a significant internal cohesion and must therefore be very carefully treated and transported. Due to their limited fiber cohesion in the steam-treated state, they can only be further shaped to a limited extend without causing thinning of the material areas tensile stressed during molding, with the accompanying loss of fiber cohesion and the tearing of the mat.
To obviate this problem, it is known (DOS No. 1,453,416) to apply to the fiber mat a reinforcing fabric which can be deformed by stretching and which is pressed into the fiber layer by the rollers used for prestrengthening the mat. Here again, the bond between the reinforcing fabric and the fiber mat is largely lost through the vapor treatment necessary prior to the final shaping. Thus, during the molding process considerable relative movements occur between the individual fibers, which can bring about the tearing of the fiber mat.
German Pat. No. 2,364,025 also discloses a fiber mat comprising two lignocellulose fibrous layers between which is placed in firmly adhering manner on a supporting layer. The pre-molded fiber mat has a plurality of regularly distributed zones of limited cross-section. This improves the adhesion of the supporting layer during vapor treatment, so that the tensile stresses occurring during molding can be better distributed in the mat. In addition, such a mat extrudate can be wound onto a reel following prestrengthening, which facilitates handling and transportation.
In order to permit the manufacture of particularly thin-walled, three-dimensional molded moldings, such as are required for the internal lining of motor vehicle interiors, a process is used (German Pat. No. 2,338,650) in which the fiber mat is gradually molded in a mold equipped with a plurality of force plugs which can be operated in time sequence. This gradual molding is necessary to prevent tearing of the fiber mat. In this process, the fiber mat is gradually fed to the deformation points without any tearing of the fibers. This known process used in the three-dimensional shaping of thin-walled moldings requires especially careful application due to the sensitivity of the fiber mats. It also requires a large amount of time due to the gradual, succesive molding.
A further disadvantage of the known process is that the fiber mats must be made from top-quality wood fiber materials if they are to have satisfactory deformation characteristics, particularly in connection with the necessary small wall thickness of the moldings. It is impossible to pass below a lower fiber length limit if the tearing of the fiber mat is to be avoided during deformation. It is therefore impossible to use shorter fibers, such as are obtained in the preparation of waste materials, for example waste paper, although the waste materials have completely satisfactory material characteristics, particularly in the case of the admixture of longer length fibers.
The problem of the invention is to obviate the disadvantages inherent in the known fiber mats and their manufacturing processes in such a way that a fiber mat is obtained which, in the manner of a deep drawing process, can be immediately molded to a thin-walled molding without the hitherto necessary gradual molding procedure. Furthermore, through the addition of short-fiber waste material a higher strength, molded article with a smaller wall thickness can be obtained.